Generally car seats are not provided, although some limo services may do so if you arrange it in advance.
Check your local laws about what's required legally and ask yourself if you're willing to chance something happening for a minor convenience of not installing a car seat.
We are in London and we are not required to use a carseat in a cab here. As it happens, the cabs are so big here that we can fit the whole stroller in without folding it, so we just lock the breaks and go.
Re: Cab/limo
Generally car seats are not provided, although some limo services may do so if you arrange it in advance.
Check your local laws about what's required legally and ask yourself if you're willing to chance something happening for a minor convenience of not installing a car seat.